1. Field of the Invention
This invention relates to digital cordless telephones, and more particularly to a digital cordless telephone that implements an inverted code sequence cordless signaling.
2. Background of Related Art
Cordless telephones are popular consumer devices that allow a user in a home or office the freedom to stray hundreds of feet from a base station. The typical cordless telephone includes a base station that is physically connected to the user""s telephone company lines and a hand-held handset unit. The physical hard wire connection between a corded handset and a conventional telephone set is replaced by a radio frequency (RF) link.
Initially, the remote handsets of cordless telephones communicated with their base station using analog signals. In more recent years, advancements have been made with respect to cordless telephones allowing digital communications between the remote handset and its base station. The entry of cordless telephones into digital communications generally provides better voice quality because of increased noise rejection, and a somewhat higher range. However, the increased voice quality and higher range involves using many more components and an increasing complexity in the digital cordless telephones. Consequently, the increased components and increased complexity may result in a higher cost for the digital cordless telephone for the average consumer.
FIG. 6A shows relevant features of a conventional frequency hopping digital remote handset 600 of a digital cordless telephone. In FIG. 6A, the remote handset 600 includes a controller 605, a radio frequency (RF) transceiver 610, a coder-decoder (CODEC) 615, a microphone 620, a speaker 625 and a spread spectrum module 630.
The controller 605 may be a digital signal processor (DSP), microprocessor, or microcontroller. The controller 605 provides an execution platform for a software program that operates the remote handset 600.
The RF transceiver 610 provides a RF interface between the remote handset 600 and a base station. The remote handset 610 relays voice signals between a base station via RF link. The RF transceiver 610 provides a conversion between RF signals and the digitized voice signals.
The CODEC 615 provides a way to convert between the analog voice signals and the digital voice signals. The CODEC 615 is typically an electronic device that converts analog voice signals to digital voice signals via an analog-to-digital converter (not shown). Also, the CODEC 615 converts received digital voice signals to analog voice signals via a digital-to-analog converter (not shown).
The microphone 620 provides a way for the user to input voice signals into the remote handset 600.
The speaker 625 provides a way for the user to hear the output voice signals from the remote handset 600.
The spread spectrum module 630 provides a way for the remote handset 600 to convert between digital voice signals into a spread spectrum digital voice signal.
The spread spectrum module 630 includes an error-correcting module 635, a digital frequency synthesizer 640, a transmitting frequency multiplier 650, a pseudo-noise (PN) code generator 645, a clock 655, a receiving frequency multiplier 660, a mixer 662, a message demodulator 670, a early-late gate module 665, a code loop module 675, and an error correction module 680.
In the transmit direction, a microphone 620 outputs an analog signal to the CODEC 615 which converts the microphone input signal to a digital microphone signal. The digital microphone signal is inputted to the spread spectrum module 630 for encoding into a spread spectrum digital signal.
The digital microphone signal is initially passed to the error correcting module 635 of the spread spectrum module 630 to provide a way to reconstruct the digital microphone signal if there are any errors during transmission to a base station.
After the error-correcting module 635, the digital microphone signal is passed to the digital frequency synthesizer 640. The digital frequency synthesizer 640 provides a way to produce another frequency from a reference signal based on an input control word. In this particular embodiment, the input control word may be m bits long. In the input control word, one of the m bits is part of the digital microphone signal and the PN generator 645 supplies the rest of the (mxe2x88x921) bits. The PN generator 645 supplies the (mxe2x88x921) bits in a PN sequence, which is passed to the digital frequency synthesizer 640. The digital frequency synthesizer 640 then generates a new signal in one of the M frequencies, where M=2m. Thus, the digital microphone signal is mapped into one of M=2m frequencies.
The mapped digital microphone signal is then passed to the transmitting frequency multiplier 650. The transmitting frequency multiplier 650 processes the mapped digital microphone signal into yet another frequency. The frequency multiplication is used to increase the processing gain and bandwidth of the mapped digital microphone signal. The output of the transmitting frequency multiplier 650 is then a spread spectrum digital signal ready for transmission.
The spread spectrum digital signal is transmitted by a RF transceiver 610 to a complementary base station 600xe2x80x2 shown in FIG. 6B.
Referring back to FIG. 6A, in the receive direction, the RF transceiver 610 receives a RF digital spread spectrum signal from the complementary base station 600xe2x80x2. The RF transceiver 610 translates the RF digital spread spectrum signal to a digital spread spectrum signal. The RF transceiver 610 then passes the spread spectrum digital signal to the spread spectrum module 630 for further processing.
The digital spread spectrum signal is multiplied by an identical signal from the PN generator 645 used during the transmission of the digital spread spectrum signal at the mixer 662. The PN generator 645 supplies (mxe2x88x921) bits in a PN sequence to the receiving frequency multiplier 660. The receiving frequency multiplier 660 generates the identical signal used during the transmission of the digital spread spectrum signal which is then sent to the mixer 662 to be processed with the incoming digital spread spectrum signal.
The resulting digital signal from the mixer 662 is a binary frequency shift keyed (FSK) signal. The message demodulator 670 demodulates the resulting digital signal. The message demodulator 670 is typically an FSK-type demodulator.
The demodulated digital signal is then passed to the error correction module 680 to recover the original digital signal. The timing synchronization in the receive path is controlled by the early-late gates 665 which controls the clock frequency.
The decoded digital signal is driven to the CODEC 615 as input. The CODEC 615 converts the digital signal to an analog signal to drive the speaker 625.
The base station 600xe2x80x2, shown in FIG. 6B, contains circuitry which is complementary to that contained in the remote handset 100, i.e., a complementary RF transceiver 610xe2x80x2, a controller 605xe2x80x2, a CODEC 615xe2x80x2, and a spread spectrum module 630xe2x80x2. The base station 600xe2x80x2 also includes a telephone line interface 690 to interface with a public switched telephone network.
Although digital spread spectrum cordless telephones operate adequately; a limiting factor in their popularity is their cost. In implementing spread spectrum techniques, there may be a larger number of components used in the digital cordless telephones. With the increased the number of components, there is a corresponding increase in the cost of the telephone.
Another cost factor, which may push the price of the digital spread spectrum cordless telephone, is the implementation of a cordless signaling protocol. The cordless signaling protocol is used to implement typical commands such as xe2x80x98Talkxe2x80x99, xe2x80x98Ringxe2x80x99, xe2x80x98Flashxe2x80x99, and etc. The command generation and processing may introduce additional hardware into the digital spread spectrum cordless telephone.
FIG. 7 illustrates a conventional command code 700 used in a conventional signaling protocol between the handset 600 and base station 600xe2x80x2. As shown in FIG. 7, the conventional command code 700 may be in a packet format. The command code includes bit synchronizing (BSYN) bits 710, frame synchronizing (FYSN) bits 720, system identifying (SYID) bits 730, error correcting code (ECC) bits 740, and control (CTRL) bits 750.
The BSYN bits 710 provide a bit level synchronizing between the handset 600 and base station 600xe2x80x2.
The FSYN bits 720 provide a command frame level synchronizing between the handset 600 and base station 600xe2x80x2.
The SYID bits 730 provide a way for the handset and base station to identify each other. Typically, the handset 600 and base station 600xe2x80x2 are a paired set. In the event that there are other digital cordless telephones in the area, the SYID 730 provide that commands sent between a paired set of the handset and base station are processed the paired set.
The ECC bits 740 provide a way to correct for errors in the command code between the handset 600 and the base station 600xe2x80x2.
The CTRL bits 750 provide a way to indicate which function or command to implement.
When the handset 600 or base station 600xe2x80x2 receives a command code 700, the controller, 605 or 605xe2x80x2, respectively, synchronizes the incoming code on a bit and frame level by using the BSYN bit 710 and FSYN bits 720. The receiving controller, 605 or 605xe2x80x2, decodes the received SYID bits 730 match the receiving SYID. If there is no match, the command code 700 is discarded. Otherwise, the command code 700 is checked for errors by processing the ECC bits 740, and the CTRL bits 750 are executed.
In order to implement the conventional signaling protocol, additional hardware, such as microcontrollers, microprocessors, memory, registers, and etc., are included in the digital spread spectrum cordless telephone. The inclusion of additional hardware may increase the costs of the digital spread spectrum cordless telephone. Thus, implementing a cordless signaling protocol between remote handset and base station may also increase the cost of the digital spread spectrum cordless telephone.
There is a need for a digital cordless telephone that offers the benefits of spread spectrum technology at a reduced cost.
In accordance with the principles of the present invention, a method for cordless signaling in a digital cordless telephone is disclosed. The method comprises transmitting a signal from a transmitter of the digital cordless telephone, inducing a signaling state from the signal in a receiver of the digital cordless telephone, and decoding a command from the signal.
A system for cordless signaling in a digital cordless telephone is disclosed. The system comprises a transmitter, a receiver, and a receiving detector; and a receiving controller. The receiving controller, receiving a signal transmitted from the transmitter, decodes a command from a signaling state induced by the signal in the receiving detector located in the receiver.
Another aspect of the present invention, a receiver for cordless signaling from a transmitter in a digital cordless telephone is disclosed. The receiver comprises a code detector, a receiving radio frequency (RF) transceiver, and a receiving controller. The receiving controller, upon receiving a signal from the RF transceiver, decoding a command from the transmitter if the code detector detects a signaling state from the signal.
Another aspect of the present invention, a transmitter for cordless signaling to a receiver in a digital cordless telephone is disclosed. The transmitter comprises a transmitting signal converter, a spreader; and a transmitting controller. The transmitting controller generates a command by pulsing an output of the transmitting signal converter to an input of the spreader.